Dynamically fill color in a gameobject?

I need to fill color in a GameObject when somebody hovers over it. How should i go about filling the GameObject with different another color to change the color at once i would use,

 Material newMaterial = new Material(Shader.Find("shadername")); 
 newMaterial.color = whateverColor;
 gameObjectRenderer.material = newMaterial ;

but i can't figure out how to animate color filling.

Example of what i want:

• Unhovered gameobject will look like

• Then when somebody hovers over it, the color will start to fill and a event will be executed when the game-object is filled completely.